The present invention relates to a filter for diesel fuel which is normally interconnected between a feeding connection connected to a fuel containing tank and a discharge connection leading to a fuel injection pump.
The filter of the type under consideration is disclosed in DE-OS No. 3,330,057. This known filter is provided with a device for a temperature responsive switching of overflow fuel quantities of the fuel injection pump and also with a ventilation device for carrying off gases from the overflow quantities returned to the tank. The disadvantage of the known filter resides in that the filter is designed as a number of interchanged components in which if the filter element becomes contaminated the filter cartridge is removed from the cover, provided with fuel connections, and exchanged. Devices for temperature responsive switching and for the ventilation are accommodated in the cover which has four fuel connections and which is rigidly mounted in the casing of the vehicle and can not be interchanged. The disadvantage resides in that the device for temperature responsive switching of overflow quantities, which is very expensive, operates with the valve which is controlled by a float gauge measuring the density of the recycled fuel. A thermostat valve for temperature responsive switching of fuel overflow from the fuel injection pump is connected in series with the above mentioned valve; this however results in the device with considerable hysterisis. Furthermore, a non-throttled passage of the overflow quantities from the fuel injection pump via the switching device and the ventilation device to the tank is often in practice disadvantageous. The cover of the filter with interchangeable components is expensive in manufacture and is not suitable for the filter to be arranged in a conduit between the tank and the injection pump, which could be removed and thrown away and replaced by a new one.
A conduit filter disclosed in GB-PS No. 1,584,517 has a cover provided with a feeding connection and a discharge connection and a cup-shaped housing which accommodates a filter element and is non-releasably connected to the cover, and in which the filter element if contaminated can be interchanged as a whole. This known filter is simple, inexpensive and compact; however it has no temperature responsive switching device and no ventilation device.
From U.S. Pat. No. 4,574,762 a temperature responsive switching device for reversing overflow quantities of a diesel fuel injection pump is known, this device operating hysteresis-free and wear-free. Effective heat of the diesel fuel is utilized to avoid wax crystallization at low temperatures. This device is provided with a bimetallic snapping disc which operates as a movable control member of a reversing valve and has a throttle opening for a continual ventilation, arranged parallel to that control member, and a pressure control valve which is open to the contaminated side of the filter. The known device is accommodated in the housing which is connected to the cover of the filter having interchangeable components by means of hollow bolts. The device is therefore not suitable as a conduit filter which should be compact and disposable.